1. Field of the Invention
The invention generally relates to carbon nanotube semiconductor devices, and, more particularly, to a carbon nanotube field effect transistor that is configured to overcome intrinsic ambipolar properties and to allow for threshold voltage adjustments and to complementary carbon nanotube devices that incorporate such transistors.
2. Description of the Related Art
A carbon nanotube (i.e., nanoscale hollow graphite tube) can, depending on its conformational geometry, exhibit either metallic or semiconductor properties. In recent years the use of semiconductor carbon nanotube (CNT) devices, such as CNT field effect transistors (CNTFETs), has been proposed to overcome scaling limits encountered by silicon semiconductor devices. Additionally, since semiconductor CNTs exhibit high transconductance, a desirable property for complementary devices, such as complementary inverters, complementary CNTFET circuitry which mimics complementary metal oxide semiconductor (CMOS) technology has been proposed. However, there are two basic barriers to doing so. First, CNTs form intrinsically ambipolar FETs due to the formation of Schottky-Barrier contacts at the junction of the source and drain electrodes and the CNT. Second, since the threshold voltage (Vt) of CNTFETs are not easily controlled via conventional means, such as doping of the channel, some means is required to adjust the threshold voltages to complementary CNTFETs-compatible values. Therefore, it would be advantageous to provide a CNTFET, and more particularly, a complementary CNT device incorporating carbon nanotube transistors that are configured to overcome intrinsic ambipolar properties and to allow for threshold voltage adjustments.